(1). Field of the Invention
The present invention relates to a thermochemical reactor for a cooling and/or heating apparatus including at least one reagent unit capable of absorbing, by chemical combination, a gas flow coming from a tank and of desorbing this gas flow by reverse chemical reaction, under the action of a rise in temperature, so that it reintegrates into said tank, said reagent unit being arranged in a container connected to said tank through a pipe, and having walls, at least some of which include diffuser means permitting to distribute the gas flow in one direction or in the other one between the reagent unit and the tank, said reagent unit being of the type capable of expanding during the absorption of the gas flow and of retracting during the desorption of the gas flow and being connected to heating means.
The invention also relates to a cooling and/or heating apparatus including such a thermochemical reactor as well as an isothermal device provided, in turn, with said cooling and/or heating apparatus.
The present invention more specifically relates to the field of the production of cold and/or heat from thermochemical systems.
(2). Description of the Prior Art
In a known way, such systems are based on heat transfers resulting from a chemical reaction between a gas, such as ammonia, and reactive salts, such as calcium chlorides, contained respectively in two tanks separated by a valve. When the latter opens, a chemical reaction occurs, during which the gas vaporizes, in order to join the salts. This evaporation is heat-consuming and therefore generates a production of cold at the level of the tank containing the gas. Furthermore, the chemical reaction between the gas and the salts is exothermic and causes heat to be released at the level of the salt tank.
After complete evaporation of the gas, or when the salts are saturated, the chemical reaction stops as well as the production of cold and heat. It is then possible to regenerate the system, simply by heating the reactive salts, which causes the separation of the salts and the gas which then returns to its original tank where it is again condensed. After regeneration of the reactive salts, a new cooling and/or heating cycle can be performed.
The progressive implementation of these thermochemical systems in an industrial environment has at the same time required the development of suitable apparatuses, having means capable of optimizing, improving and controlling the evolution of the thermochemical reactions, and designed by means of reliable materials capable of withstanding high stresses, namely pressure and temperature stresses.
In this context, many work related to the development of the reactor, i.e. the unit formed by the reactive salts, the envelope in which they are contained and the various means the latter is provided with, with a view to providing a solution in which the reagent is not only capable of absorbing and desorbing a maximum quantity of gas without being carried along by this gas, but also capable of undergoing volume changes in said envelope, without deteriorating same or losing its reactive qualities, even bursting.
Presently, several documents are known, which are dedicated to the description of innovations made in this field.
Thus, FR 2 455 713 for example refers to a thermochemical reactor, which can be formed of several reactive bodies made self-supporting by a binder and contained in a flexible envelope having several envelope elements. Passages provided for between adjacent envelope elements define channels allowing the gas flow to circulate between the various reactive bodies. The reactor also includes distribution structures which communicate with the circulation channels and are designed so as to be adapted to the dimensional changes of an envelope element. These distribution structures can include telescopic elements which can be pushed into each other in order to cause changes in length of said distribution structures.
Such a thermochemical reactor has the disadvantage of a complex structure characterized by a great brittleness.
U.S. Pat. No. 2,649,700 describes a thermochemical reactor including several annular-shaped elementary reagent units confined between an inner wall and a peripheral wall. Porous screens separating the elementary units from each other distribute the gas flow between the lower and higher surfaces of the latter and an inlet and outlet conduit. The elementary units are made out of sintered metal and are thus dimensionally stable, namely as regards the above-mentioned pressure and temperature stresses.
Practice has shown that this embodiment has many disadvantages. Indeed, the metallic nature of the units highly limits the quantity of gas that can be absorbed and is in addition characterized by poor retention of the absorbing particles. This obliges to cause the gas flow to pass too fast through screens acting as filters, which complicate the structure of the unit and make it heavy.
From EP 0 206 875 is also known a reagent unit formed by a mixture of chloride and an foamed carbon derivative, capable of absorbing high quantities of gas per volume of unit, and solving the problem of mass transfer. This solid reagent unit has however a low mechanical strength that tends to quickly be deformed under the action of pressure gradients and volume changes it undergoes, so that its gas retention capability gradually tends to decrease during the cooling-regeneration cycles. Finally, the surfaces of the reagent for the mass exchanges can be deformed so much that they become completely ineffective.
In the solution provided by U.S. Pat. No. 2,384,460, the reactive material is confined between containment walls, in a limited volume, and through same pass perforated gas conduits filled with glass wool aimed at retaining said reactive material. Because of the close confinement, the reactive material maintains the same volume and the same shape, not only during the saturation phase, but also during the successive absorption-desorption cycles.
A quite similar thermochemical reactor device is also provided in EP 0 692 086, which describes namely a thermochemical reactor including a solid reagent unit confined in a container, between containment walls, some of which are pervious to mass exchanges. The characteristic of this reactor is defined by the reagent unit used being likely to undergo changes in volume depending on the quantity of gas absorbed, while the containment walls are capable of ensuring the stability in shape of the unit against the tendency to said changes in volume. Thus, in this document is provided to enclose a solid reagent unit in a container with strictly adapted dimensions, so that this reagent unit maintains its dimensions during the various absorption-desorption cycles, maintains its initial mechanical strength, and avoids its swelling, even its deterioration through bursting.
It could be observed that confining the reagent inside a limited space, as described in particular in the last two documents, although made necessary in order to avoid the deterioration of the system, in particular in order to avoid bursting of the reagent unit, represents an obstacle to an optimal evolution of the expected thermochemical reactions. Indeed, impeding the swelling of the reagent considerably reduces the maximum quantity of gas which can be successively absorbed and desorbed, which has in particular a repercussion on the time of autonomy of the system.
Another known similar device is described in the document FR 2 723 438 and tries to cope with the separation of the solid reagent from the walls of the enclosure, this separation resulting into a loss of the power of the reaction through a drop in the thermal-transfer coefficient. To this end, a fluid is introduced between the reagent and the walls of the enclosure, said fluid bringing about the thermal connection between the reagent and the enclosure. In addition, a fluid-confining device is added inside the enclosure in order to limit the displacement of said fluid and to prevent it from accumulating on top of the reagent.
This device has nevertheless the disadvantage of being of a complex embodiment, using additional means for implementing a fluid and for confining same.